1. Field of the Invention
The present invention relates to a device and a method of etching an elements such as semiconductor elements or LCD substrate.
2. Description of the Related Art
More and more attention has been paid these days to the plasma etching device which etches various kinds of thin film, using components reacting in gas plasma. This is because this device helps to simplify and automate the complicated process of semiconductor manufacturing elements, and to form micropatterns with high accuracy.
A plasma etching device of this type is disclosed in, for example, Japanese Patent Disclosure No. 57-156034. In this plasma etching device. a lower electrode made of aluminium is located under an air-tight vessel which is set side by side with a vacuum means, and an upper electrode made of amorphous carbon and supported by an electrode body made of, for example, aluminium, is located above and opposite to the lower electrode. The upper and lower electrodes are connected to an RF power source. An object to be processed, for example, a semi-conductor wafer, is placed on the lower electrode. Power is supplied from the RF power source to both electrodes, and process gas is supplied into the gap between the electrodes, while keeping the gap in vacuum. The process gas is forced into plasma by the power supplied, and the surface of the object to be processed is etched by the plasma.
To place the semiconductor wafer on the lower electrode, the upper electrode is lifted to have a certain clearance with respect to the lower electrode. The semiconductor wafer, which has been carried by a carrier means such as the robot hand, is placed on the lower electrode and the upper electrode is then lowered, thus defining a predetermined gap between it and the lower electrode.
In the case of this device, the upper electrode is moved up and down. The system for driving the upper electrode is therefore located above the level at which the wafer is located. This causes dust, generated by this drive system, to adhere to the wafers being carried outside the vacuum atmosphere or those housed in cassettes. The dust on wafers imposes undesirable influence on micropatterns of highly integrated circuits formed on wafers, thereby lowering the efficiency of the etching process.
In order to eliminate this drawback, there has been proposed a device designed to move the lower electrode and to locate the system of driving the lower electrode below that level at which the wafer is placed (see preliminarily-opened Japanese Utility Model Application Sho 56-43158). In the case of this second device, however, the gap between the semiconductor wafer placed on the lower electrode and the upper electrode cannot always be constant. This prevents uniform etching.
A clamp ring for holding a wafer can be located between the upper and lower electrodes, thereby to maintain an uniform gap between the upper electrode and the wafer (see U.S. Pat. No. 4,615,755). The use of such a clamp ring is disadvantageous in two respects. First, since the system for driving the clamp ring is located above the wafer, the dust raised by this system is likely to lie on the wafer. Secondly, the gap formed between the wafer and the upper electrode is not sufficiently uniform.